The present invention generally relates to magnetic sensors. The present invention also relates to magnetic sensors for sensing the speed and direction of a rotating target. The present invention additionally relates to differential Hall sensors. In addition, the present invention relates to sensors utilized in automotive applications, including transmission, crank/cram, and wheelspeed mechanisms thereof.
Various sensors are known in the magnetic effect sensing arts. Examples of common magnetic effect sensors include Hall effect sensors, differential Hall sensors, and magnetoresistive sensor technologies. Such magnetic sensors can respond to the change of magnetic field as influenced by the presence or absence of a ferromagnetic target object of a designed shape passing by the sensory field of the magnetic effect sensor. The sensor can then provide an electrical output signal, which can be further modified as necessary by subsequent electronics to yield appropriate sensing and control information thereof. Associated electronics may be either onboard or outboard of the sensor package.
Geartooth sensors, for example, are known in the automotive arts to provide information to an engine controller for efficient operation of the internal combustion engine. One such known arrangement involves the placing of a ferrous target wheel on the crankshaft of the engine with the sensor located proximate thereto. The target objects, or features, i.e., tooth and slot, are, of course, properly keyed to mechanical operation of engine components. Such sensors can be configured according to the Hall effect, which is well known in the magnetic sensor arts.
The Hall effect has been known for many years. Hall effect sensors are typically based on the utilization of a Hall generator, which generally comprises a magnetic field dependent semiconductor whose function rests on the effect discovered by Edwin Hall. This effect, known as the xe2x80x9cHall effect,xe2x80x9d is caused by the Lorentz force, which acts on moving charge carriers in a magnetic field.
One of the first practical applications of the Hall effect was as a microwave power sensor in the 1950s. With the later development of the semiconductor industry and its increased ability for mass production, it became feasible to use Hall effect components in high volume products. In 1968, Honeywell""s MICRO SWITCH division produced a solid-state keyboard using the Hall effect. The Hall effect sensing element and its associated electronic circuit are often combined in a single integrated circuit.
In its simplest form, a Hall element can be constructed from a thin sheet of conductive material with output connections perpendicular to the direction of electrical current flow. When subjected to a magnetic field, the Hall effect element responds with an output voltage that is proportional to the magnetic field strength. The combination of a Hall effect element in association with its associated signal conditioning and amplifying electronics is sometimes called a Hall effect transducer.
A comprehensive source of information about Hall effect devices is provided in a book by R. S. Popovic, entitled xe2x80x9cHall Effect Devices: Magnetic Sensors and Characterization of Semiconductorsxe2x80x9d, published under the Adam Hilger Imprint by IOP Publishing Limited.
In the differential Hall sensor, two Hall generators may be arranged close to one another. The individual Hall generators operate along the same principle as the magnetic dependent semiconductor in single Hall effect sensors. Both Hall elements are generally biased with a permanent magnet.
Transmission manufacturers generally desire a single sensor to sense the speed and direction of a transmission mechanism. Comparing two output signals and determining which output signal leads or lags the other, with a desired phase between the two signals of approximately 90 degrees, can obtain direction information. Speed information can be obtained by monitoring an associated pulse width or period width of one of the output signals. Differential Hall analog signals often become non-sinusoidal as target features increase. Varying target rotation direction can thus cause large errors in signal phasing when comparing dual differential Hall digital outputs, because of the association non-symmetry of the analog signals. The present inventor has thus concluded, based on the foregoing, that a need exists for an apparatus and method for eliminating such errors, particularly during phase shifts from sinusoidal to non-sinusoidal phases. A unique apparatus and method for eliminating such errors is, therefore, disclosed and described herein.
The following summary of the invention is provided to facilitate an understanding of some of the innovative features unique to the present invention and is not intended to be a full description. A full appreciation of the various aspects of the invention can be gained by taking the entire specification, claims, drawings, and abstract as a whole.
It is one aspect of the present invention to provide an improved sensor method and apparatus for sensing the speed and direction of a rotating target.
It is also an aspect of the present invention to provide an improved differential Hall sensor method and apparatus.
It is yet another aspect of the present invention to provide an improved sensor method and apparatus for determining the phase stability of non-sinusoidal signals utilizing two differential Hall packages.
The above and other aspects can be achieved as is now described. A method and apparatus for sensing the speed and direction of a rotating target are disclosed herein. A first differential Hall package is generally located opposite a second differential Hall package, wherein the first differential Hall package and second differential Hall package comprise mirror images of one another. The first differential Hall package generally includes two magnetic Hall elements. Similarly, the second differential Hall package generally includes two magnetic Hall elements. Such magnetic Hall elements may comprise differential Hall elements. A first output signal can is generated by the first differential Hall package, and a second output signal is generated by the second differential Hall package during a rotation of the rotating target. The first Hall output signal can thus be compared to the second Hall output signal during a shift of the rotating target from a sinusoidal phase to a non-sinusoidal phase thereof, thereby permitting accurate phase information indicative of the speed and direction of the rotating target to be obtained.
The present invention thus comprises a speed and direction sensor that generally utilizes two separate differential Hall packages, which each may be implemented as integrated circuit (IC) packages. An initial phase can be established by the distances between each of the IC packages as a function of the target and magnet placements thereof. Differential Hall analog signals become non-sinusoidal as target features increase. Changing the target rotation direction causes large errors in signal phasing when comparing dual differential Hall digital outputs because of the non-symmetry of the analog signals. To eliminate the large resulting error, IC package placement relative to one another is thus critical. By placing the IC packages in opposite directions relative to each other, the associated phase remains unaffected by the target rotation. If both IC packages are placed in the same direction, however, a large phase shift will be seen when the target rotation is varied.
The method and apparatus for placing differential Hall elements next to one another as described herein thus becomes beneficial when the Hall output (i.e., analog signal) begins to alter from a perfect sinusoidal signal. When target features are wide, for example, with respect to the target-to-sensing plane and the sensing plane-to-magnet distances, the Hall signal tends to posses areas of xe2x80x9cleveling offxe2x80x9d or an area of decreased slope. This area greatly impacts how the two signals optimally can be compared to one another to achieve the most accurate phase information between target rotations. The sensor method and apparatus thus disclosed herein can be utilized for any application where target direction is required, thereby yielding the best signals.